1. Field of the Invention
The present invention relates to an encoding-decoding method for optical pulses, an optical pulse time spreading apparatus used in optical multiplexing transmission, an optical add-drop-multiplexer (ADM) using the optical pulse time spreading apparatus, and an optical communication system using the ADM.
2. Description of the Related Art
In these years, there is a rapidly increasing demand for communications due to the widespread use of the Internet, and accordingly communication capacity is being rapidly increased. Also, communication systems in a wide variety of forms are being constructed, and communication networks equipped with an ADM capable of large-capacity transmission and in a flexible bus or ring form are being actively proposed and researched.
Attracting attention as a technique for increasing communication capacity are optical multiplexing technologies that transmit optical pulse signals for multiple channels together over a single optical fiber transmission line. Among the optical multiplexing technologies, an optical time division multiplexing (OTDM) scheme, a wavelength division multiplexing (WDM) scheme, and an optical code division multiplexing (OCDM) scheme are being actively researched.
Because any of these optical multiplexing technologies can transmit optical pulse signals for multiple channels together over a single optical fiber transmission line, with existing communication networks remaining as they are, a great increase in communication capacity can be provided. Further, by combining these optical multiplexing technologies, a further great increase in communication capacity can be realized. For example, a combined multiplexing transmission system of the OCDM scheme and the TDM scheme is being studied. Refer to, for example, Klaus Grobe, Jorg-Peler Elbers, “PON Evolution from TDMA to WDM-PON”, OFC NThD6 (2008) (hereinafter, referred to as Non-patent document 1). Or, a combined multiplexing transmission system of the OCDM scheme and the WDM scheme is being studied. Refer to, for example, Taro Hamanaka, Xu Wang, Naoya Wada, and Ken-ich Kitayama, “Demonstration of 16-user OCDMA over 3-wavelength WDM using 511-chip, 640 Gchip/s SSFBG en/decoder and single light source”, OFC OMO1 (2007) (hereinafter, referred to as Non-patent document 2).